A variety of approaches are used to reduce energy consumption in buildings. Among the approaches being considered and applied is the more efficient use of sunlight to provide lighting inside buildings. One technique for supplying light inside of buildings, such as in offices, etc. is the redirection of incoming sunlight. Because sunlight enters windows at a downward angle, much of this light is not useful in illuminating a room. However, if the incoming downward light rays can be redirected upward such that they strike the ceiling, the light can be more usefully employed in lighting the room.
A variety of articles have been developed to redirect sunlight to provide illumination within rooms. A light deflecting panel is described in U.S. Pat. No. 4,989,952 (Edmonds). These panels are prepared by making a series of parallel cuts in a sheet of transparent solid material with a laser cutting tool. Examples of daylighting films include European Patent No. EP 0753121 and U.S. Pat. No. 6,616,285 (both to Milner) which describe optical components that include an optically transparent body with a plurality of cavities. Another daylighting film is described in U.S. Pat. No. 4,557,565 (Ruck et al.), which describes a light deflecting panel or plate which is formed of a plurality of parallel identically spaced apart triangular ribs on one face. Examples of films that have a plurality of prism structures are described in US Patent Publication No. 2008/0291541 (Padiyath et al.) and pending U.S. Patent Applications: Ser. No. 61/287,360, titled “Light Redirecting Constructions” filed Dec. 17, 2009 (Padiyath et al.), and Ser. No. 61/287,354, titled “Light Redirecting Film Laminate” filed Dec. 17, 2009 (Padiyath et al.).
A number of articles have been developed to scatter or diffuse light. In U.S. Pat. No. 6,608,722 (Cowan et al.), a diffuser is disclosed that transmits or reflects incident light into a specific range of angles. The diffuser consists of two parts, the first part diffracts or reflects light into a specific offset angle, the second part uniformly scatters the light through a range of angles. In U.S. Pat. No. 5,534,386 (Petersen et al.), a homogenizer for incident light includes a sheet of embossable material including one micro-sculpted surface relief structure that controls the direction in which light propogates and homogenizes light with directionality. U.S. Pat. No. 6,613,402 (Chou et al.) disclosed a rear projection screen assembly that includes a diffuser and a polarizer. The PCT Publication No. WO 00/10929 (Savant) discloses a surface light shaping diffuser by embossing or molding light shaping structures onto a high quality optical glass. Particles have been used to scatter or diffuse light. US Patent Publication No. 2008/0182958 (Lafleur et al.) describes light scattering polymer particles that have a different refractive index at the center of the particle than at the shell of the particle, and also discloses dispersing the particles in a polymeric matrix. A number of references describe light diffusing or light scattering films that comprise particles dispersed within a matrix. In U.S. Pat. No. 5,237,004 (Wu et al.) the matrix is a thermoplastic or thermoset polymer composition, in PCT Publication Nos. WO 97/01610 (Goetz et al.) and WO 2010/033571 (Sherman et al.) the matrix is a pressure sensitive adhesive, and in PCT Publication No. WO 2008/144217 (Padiyath et al.) a light diffusing solar control film includes a multilayer film that transmits visible light and reflects infrared light, and a light diffusing layer or surface. PCT Publication No. WO 2010/0297406 (Schaffer et al.) describes a light diffusing adhesive that includes an adhesive matrix and a block copolymer that forms light diffusing microdomains within the adhesive matrix. PCT Publication No. WO 2005/005162 (Hayashi et al.) describes a shading decorative sheet that includes a thermoplastic resin film with a decorative layer provided on its front face, where the decorative pattern has a gradation pattern in at least one direction.